Allan Shortlidge 9c76e0d1bf AST: Emit correct synthesized availability attributes for unownedExecutor property. ...

When synthesizing a declaration and inferring its availability, the synthesized attribute should factor in unavailability of the parent declarations. This recently regressed with https://github.com/apple/swift/pull/63361. However, the previous implementation did not produce correct results, either, because the logic for merging availability attributes produced a non-sensical result when both `unavailable` and `introduced:` availability attributes were merged. For example, this was the result for the synthesized `unownedExecutor` property of an actor when the actor was marked unavailable:

```
@available(macOS, unavailable)
actor A {
  // Incorrectly synthesized availability for `unownedExecutor` which results from merging
  // the unavailability of the parent and the availability of the UnownedSerialExecutor type.
  @available(macOS, unavailable, introduced: macOS 10.15)
  @_semantics("defaultActor") nonisolated final var unownedExecutor: UnownedSerialExecutor { get }
}
```

This is fixed by omitting all version components from the synthesized attribute when the overall attribute kind is "unavailable".

Additionally, I discovered that the `concurrency_availability.swift` test case was no longer testing what it intended to test. The conformances to `Actor` for each `actor` in the test were no longer being synthesized and therefore `unownedExecutor` was not being synthesized. That was fixed by importing the `_Concurrency` module directly, which seems to be necessary because of the `-parse-stdlib` flag in the test.

Resolves rdar://106055566

2023-03-02 10:09:30 -08:00

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